1. Field of Invention
The present invention relates to a novel triglyceride and a composition comprising the same, and more particularly, to a triglyceride having a saturated fatty acid having 16 to 18 carbon atoms at the position 2 of the triglyceride, and having a .omega.6, .omega.9 and/or (3 unsaturated fatty acids at the positions 1 and/or 3.
2. Related Art
The majority of the lipids that so far obtained are neutral fats that comprise a mixture of triglycerides in which various fatty acids are randomly ester-bonded to the positions 1, 2 and 3 of the triglyceride. These lipids were shown to demonstrate different absorption properties and physiological activities according to differences in the bonding positions of the fatty acids. Lipids in which specific fatty acids are bonded to predetermined positions of triglyceride (structured lipids) have recently attracted considerable attention.
For example, Japanese Examined Patent Publication No. 4-12920 discloses a triglyceride having satisfactory digestion and absorption property in which a fatty acid having 8 to 14 carbon atoms is bonded to the position 2 of the triglyceride and fatty acids having 18 or more carbon atoms are bonded to the positions 1 and 3. In addition, since it is known that 2-monoglycerides are of a form that is most easily absorbed by the human body, Japanese Examined Patent Publication No. 5-87497 discloses a triglyceride in which a 0)3 or 0)6 highly unsaturated fatty acid having physiological function is bonded to the position 2, while saturated fatty acids easily hydrolyzable by enzymes of the digestive tract are bonded at the positions 1 and 3. However, there is no disclosure or suggestion of the relationship between the physiological properties and the structure of triglycerides in human breast milk having unsaturated fatty acids.
On the other hand, with respect to the physiological function of fatty acids, attention has focused in recent years on arachidonic acid and docosahexaenoic acid. These fatty acids are contained in human breast milk and have been reported to be useful in infant development (Advances in Polyunsaturated Fatty Acid Research, Elsevier Science Publishers, 1993, pp. 261-264) and to be important in infant growth and brain development (Proc. Natl. Acad. Sci. USA, 90, 1073-1077 (1993), Lancet, 344, 1319-1322 (1994)).
Several official agencies have recommended intake values (premature infants: arachidonic acid: 60 mg/kg, docosahexaenoic acid: 40 mg/kg; normal infants: arachidonic acid: 20 mg/kg, docosahexaenoic acid: 20 mg/kg body weight/day (WHO-FAO (1994)). In several countries in Europe, premature infant formulas have been marketed that contain docosahexaenoic acid and arachidonic acid produced by fermentation blended as triglycerides. However, there have been no considerations given to the bonding positions of arachidonic acid and/or docosahexaenoic acid in the triglycerides added to these formulas.
The triglyceride structure in human breast milk is predicted to be such that there is a high proportion of triglycerides in which palmitic acid (16:0) is bonded to position 2 of the triglyceride, and a high proportion of triglycerides in which highly unsaturated fatty acid or medium chain fatty acid is bonded to positions 1 and 3 (Christie, W. W. (1986): The Positional Distribution of Fatty Acids in Triglycerides, Analysis of Oils and Fats, Hamilton, R. J. and Russell, J. B. eds., pp. 313-339, Elsevier Applied Science, London). However, these are merely suppositions based on the results of analysis of fatty acids in triglycerides, while isolation and structural analysis of triglycerides in human breast milk have not yet been attempted.
In addition, although triglycerides containing arachidonic acid produced by fermentation have been added to formula to allow fatty acid composition to more closely approximate the composition of human breast milk as previously described, since the structure of these triglycerides containing arachidonic acid is such that there is a high proportion of triglycerides in which palmitic acid and other saturated fatty acids are bonded at the positions 1 and 3 while unsaturated fatty acids are bonded at position 2 (J. J. Myher, A. Kuksis, K. Geher, P. W. Park and D. A. Diersen-Schade, Lipids, 31, pp. 207-215 (1996)), it is different from the structure of triglycerides hypothesized in human breast milk.
Thus, there is a strong desire to develop lipids surmised to have the glyceride structure of human breast milk, and more specifically, triglycerides reliably confirmed to have a structure in which saturated fatty acid having 16 to 18 carbon atoms is bonded at the position 2 of the triglyceride, while highly unsaturated fatty acids or medium chain fatty acids are bonded at positions 1 and 3.